Polyacetylene, (CH).sub.X, is the simplest possible conjugated organic polymer. Because of this fundamental nature, polymers of acetylene have always held special interest to polymer chemists. This interest was heightened when it was found that the electrical conductivity of poly(acetylene) could be significantly enhanced by doping the polymer with electron acceptors. See Berets et al., Trans Faraday Soc., 64 823-8 (1968).
The first polymers of acetylene were prepared in powder form. Subsequently, however, Shirakawa and others succeeded in synthesizing lustrous, silvery, polycrystalline films of poly(acetylene), and developed techniques for controlling the cistrans content of such films. See H. Shirakawa and S. Ikeda, Polym. J., 2 (1971) 231; H. Shirakawa, T. Ito and S. Ikeda, Polym. J., 4 (1973) 460; T. Ito, H. Shirakawa and S. Ikeda, J. Polym. Sci., Polym. Chem. Ed., 12 (1974) 11; and T. Ito, H. Shirakawa and S. Ikeda, J. Polym. Sci., Polym. Chem. Ed., 13 (1975) 1943.
Continued work by Shirakawa resulted in the discovery that the polycrystalline film could be doped with electron acceptors to markedly increase electrical conductivity of such films to levels characteristic of or approaching the conductivities of metals. See U.S. Pat. No. 4,222,903 to Shirakawa et al. In fact, it has now been demonstrated that chemical or electrochemical doping with electron donors or electron acceptors can increase the electrical conductivity of polycrystalline films of poly(acetylene) by over 12 orders of magnitude. Thus, the electrical conductivity of these films can range from that of an insulator ( 10.sup.-10 ohm.sup.-1 CM.sup.-1) to that of a semiconductor, to that of a metal ( 10.sup.3 ohm.sup.-1 cm.sup.-1) See Synthetic Metals 1, 101-118 (1979/80) Elsevier Sequoia S.A., Lausanne.
Unfortunately, poly(acetylene) has poor mechanical and physical properties. It is, for example, insoluble, intractable and infusable, making it difficult or impossible to process. Additionally, although polyacetylene film remains reasonably flexible if maintained in an inert atmosphere, it quickly becomes brittle upon exposure to ambient conditions.
Because of the potential offered by the unique electrical properties, much effort has been devoted to improving the mechanical and physical properties of polymers based upon acetylene. For example, substituted analogs of acetylene, such as methylacetylene and phenylacetylene, have been polymerized in the form of polycrystalline films. While these polymers of substituted acetylenes showed improved mechanical properties, their electrical conductivities were several orders of magnitude smaller than those obtainable for doped poly(acetylene). See Cukor, P., Krugler, J. I. and Rubner, M.F., Polym. Prep., Am. Chem. Soc. Div. Polym. Chem., 1980, 21 161. Poly(phenylacetylene) also showed a much more rapid decrease in electrical conductivity than poly(acetylene); in fact, catastrophic failure of poly(phenylacetylene) was found to occur in less than 250 hours of exposure to ambient conditions. See Deits, W., Cukor, P., Rubner, M. and Jopson, H., "Stability and Stabilization of Polyacetylene, Polyphenylacetylene, and Acetylene/Phenylacetylene Co-polymers," Synthetic Metals, 4 (1982) 199-210.
Previous research has also focused on efforts to produce co-polymers of acetylene, such as copolymers of acetylene with phenylacetylene or methylacetylene. See Deits, W., Cukor, P., Rubner, M., Jopson, H., Synthetic Metals, 4 (1982) 199; and Chien, J. C. W., Wnek, G. E., Karasz, F. E., Hirsch, J. A., Macromolecules, 14 (1981), 479. This work was carried out with the hope that the structure of the polymer backbone would result in unaltered electrical properties whereas the side groups would impart processing advantages. While the co-polymers were found to have some processing advantages over the homopolymer, it was unfortunately found that this was accomplished with concomittant significant decreases in electrical conductivity.
Research efforts with acetylene polymers then took another direction and focused upon blends of acetylene with other polymers. One such blend was prepared by polymerizing acetylene in solid low density polyethylene films impregnated with Ziegler-Natta catalyst. See Galvin, M. E. and Wnek, G. E., Polymer 23 (1982), 795-7. Such blends are also described and claimed in U.S. Pat. No. 4,394,304, issued to Wnek.
In order to introduce the poly(acetylene) into the polyethylene matrix, these researchers employed high polymerization temperatures (e.g., 100.degree.-110.degree. C.) for acetylene. Such high temperatures were necessary to break the crystallinity of the polyethylene so that acetylene could penetrate the polyethylene. Such high polymerization temperatures can lead to side reactions, however, such as crosslinking and chain scission reactions. Also, blends of polyacetylene and polyethylene are still relatively rigid materials because the host polymer polyethylene remains a partially crystalline material.
More recently, blends of polyacetylene with the elastomer, polybutadiene, have been described. See Rubner, M.F., Tripathy, S. K., Georger, J., Jr. and Cholewa, P., "Structure-Property Relationships of Polyacetylene/ Polybutadiene Blends," Macromolecules, 16, (1983) 870-5. While polybutadiene and other conventional elastomers, may add flexibility to such blends, they are typically not suitable host polymers for poly(acetylene). This is due to the fact that such polymers generally require post-curing processes subsequent to blend preparation. These curing processes typically require heat and harsh chemicals which attack the unsaturated bonds in poly(acetylene) causing a concomittant deterioration of electrical properties.